This section provides background information related to the present disclosure which is not necessarily prior art.
In view of increased consumer demand for four-wheel drive (4WD) and all-wheel drive (AWD) motor vehicles, a large number of power transfer systems are currently utilized in vehicular applications for selectively and/or automatically transmitting rotary power (i.e., drive torque) from the powertrain to all four wheels. In most power transfer systems, a power transfer assembly is used to deliver drive torque from the powertrain to one or both of the primary and secondary drivelines. The power transfer assembly is typically equipped with a torque transfer coupling that can be selectively actuated to shift operation of the power transfer system from a two-wheel drive mode into a four-wheel drive mode. In the two-wheel drive mode, drive torque is only transmitted to the primary driveline while drive torque can be transmitted to both of the primary and secondary drivelines when the vehicle is operating in the four-wheel drive mode.
In most 4WD vehicles, the power transfer assembly is a transfer case arranged to normally transmit drive torque to the rear driveline and selectively/automatically transfer drive torque through the torque transfer coupling to the front driveline. In contrast, in most AWD vehicles, the power transfer assembly is a power take-off unit (PTU) arranged to normally permit drive torque to be transmitted to the front driveline and to selectively/automatically transfer drive torque through the torque transfer coupling to the rear driveline.
Many power transfer assemblies are equipped with an adaptively-controlled torque transfer coupling to provide an “on-demand” power transfer system operable for automatically biasing the torque distribution ratio between the primary and secondary drivelines, without any input or action on the part of the vehicle operator, when traction is lost at the primary wheels. Modernly, such adaptively-controlled torque transfer couplings are equipped with a multi-plate clutch assembly and a power-operated clutch actuator that is interactively associated with an electronic traction control system having a controller unit and a plurality of vehicle sensors. During normal operation, the clutch assembly is maintained in a released condition so as to transmit drive torque only to the primary wheels and establish the two-wheel drive mode. However, upon detection of conditions indicative of a low traction condition, the power-operated clutch actuator is actuated to frictionally engage the clutch assembly and deliver a portion of the total drive torque to the secondary wheels, thereby establishing the four-wheel drive mode.
In virtually all power transfer systems of the types noted above, the secondary driveline is configured to include a propshaft, a drive axle assembly, and one or more constant velocity universal joints. Typically, the opposite ends of the propshaft are drivingly interconnected via the constant velocity universal joints to a rotary output of the torque transfer coupling and a rotary input to the drive axle assembly. In most instances, this rotary input is a hypoid gearset used to transmit drive torque from the propshaft to a differential gear mechanism associated with the drive axle assembly. The differential gear mechanism may include a differential carrier rotatably supported in an axle housing and which drives at least one pair of bevel pinions which, in turn, are commonly meshed with first and second output bevel gears. The first and second output bevel gears of the differential gear mechanism are drivingly connected to corresponding first and second axleshafts which, in turn, drive the secondary wheels. The hypoid gearset includes a pinion gear meshed with a ring gear. The pinion gear is typically formed integrally with, or fixed to, a solid pinion shaft that is also rotatably support by the axle housing. The pinion shaft is usually connected via one of the constant velocity universal joints to the propshaft while the ring gear is usually fixed for rotation with the differential carrier of the differential gear mechanism. Due to the axial thrust loads transmitted through the hypoid gearset, it is common to utilize at least two laterally-spaced tapered bearing assemblies to support the pinion shaft for rotation relative to the axle housing.
Many constant velocity (CV) joints are sealed in order to retain lubricant, such as grease, inside the joint while keeping contaminants and foreign matter, such as dirt and water, out of the joint. To achieve this protection, the CV joint is typically enclosed at the open end of its outer race by a sealing boot made of rubber or urethane. The opposite end of the outer race is sometimes formed by an enclosed dome or grease cap. Such sealing is necessary since once the inner chamber of the CV joint is partially-filled with the lubricant, it is generally lubricated for life. It is often necessary to vent the CV joint in order to minimize air pressure fluctuations which result from expansion and contraction of air within the joint during operation. This is especially true, for example, in tripod-type, plunging and monoblock types of joints.
Plunging tripod CV joints are widely used in 4WD and AWD vehicles and provide a plunging end motion feature which allows the interconnected rotary components to change length during operation without the use of splines. Plunging “cross-groove” types of CV joints are also commonly used to interconnect the pinion shaft of the hypoid gearset in the drive axle assembly to the propshaft and include balls located in the circumferentially-spaced straight or helical grooves formed in the inner and outer races. Typically, CVJ's are vented by placing a vent system in the housing, such as a vent hole, to allow passage of air into and out of the joint, as needed, to prevent internal pressure buildups. Unfortunately, grease may eventually block the air passage through the vent hole which could lead to reduced service life of the lubricated for life joints.
While such conventional drive axle assemblies and pinion shaft support arrangements are adequate for their intended purpose, a need still exists to advance the technology and structure of such products to provide enhanced configurations that provide improved efficiency, reduced weight, and reduced packaging requirements.